性能改善之For与Foreach

关于For与Foreach的区别，博客园里已经有好多这样文章了，都分析的挺好：http://www.cnblogs.com/jobs/archive/2004/07/17/25218.aspx  不过里面关于安全部分的描述可以略过。

以下是我的测试代码：

using System;

using System.Collections.Generic;

using System.Collections;

using System.Linq;

using System.Text;

using System.Diagnostics;

namespace ConApp_PerformanceTest

{

    class Program

    {

        static void Main(string[] args)

        {

            string[] timeperiod = new string[10];

            timeperiod[0] += "testArrayListWithFor    ";

            timeperiod[1] += "testArrayListWithForEach";

            timeperiod[2] += "testArrayWithFor        ";

            timeperiod[3] += "testArrayWithForEach    ";

            timeperiod[4] += "testListWithForEach     ";

            timeperiod[5] += "testListWithFor         ";

            for (int i = 0; i < 6; i++)

            {

                Stopwatch sw = new Stopwatch();

                TestData td = new TestData();

                sw.Reset();

                sw.Start();

                td.testArrayListWithFor();

                sw.Stop();

                timeperiod[0] += "    " + sw.ElapsedMilliseconds.ToString("00000");

                sw.Reset();

                sw.Start();

                td.testArrayListWithForEach();

                sw.Stop();

                timeperiod[1] += "    " + sw.ElapsedMilliseconds.ToString("00000");

                sw.Reset();

                sw.Start();

                td.testArrayWithFor();

                sw.Stop();

                timeperiod[2] += "    " + sw.ElapsedMilliseconds.ToString("00000");

                sw.Reset();

                sw.Start();

                td.testArrayWithForEach();

                sw.Stop();

                timeperiod[3] += "    " + sw.ElapsedMilliseconds.ToString("00000");

                sw.Reset();

                sw.Start();

                td.testListWithForEach();

                sw.Stop();

                timeperiod[4] += "    " + sw.ElapsedMilliseconds.ToString("00000");

                sw.Reset();

                sw.Start();

                td.testListWithFor();

                sw.Stop();

                timeperiod[5] += "    " + sw.ElapsedMilliseconds.ToString("00000");

            }

            Console.Clear();

            for (int i = 0; i < 10; i++)

                Console.WriteLine(timeperiod[i]);

            Console.Read();

        }

    }

    class TestData

    {

        public TestData()

        {

        }

        public void testArrayListWithFor()

        {

            ArrayList sa;

            object ss;

            sa = new ArrayList();

            for (int i = 0; i < 10000000; i++)

                sa.Add("This is a string");

            for (int i = 0; i < 1000000; i++)

                ss = sa[i];

        }

        public void testArrayListWithForEach()

        {

            ArrayList sa;

            string ss;

            sa = new ArrayList();

            for (int i = 0; i < 10000000; i++)

                sa.Add("This is a string");

            foreach (string s in sa)

                ss = s;

        }

        public void testListWithForEach()

        {

            List<string> sa;

            string ss;

            sa = new List<string>();

            for (int i = 0; i < 10000000; i++)

                sa.Add("This is a string");

            foreach (string s in sa)

                ss = s;

        }

        public void testListWithFor()

        {

            List<string> sa;

            string ss;

            sa = new List<string>();

            for (int i = 0; i < 10000000; i++)

                sa.Add("This is a string");

            for (int i = 0; i < 10000000; i++)

                ss = sa[i];

        }

        public void testArrayWithFor()

        {

            string[] sa;

            string ss;

            sa = new string[10000000];

            for (int i = 0; i < 10000000; i++)

                sa[i] = "This is a string";

            for (int i = 0; i < 10000000; i++)

                ss = sa[i];

        }

        public void testArrayWithForEach()

        {

            string[] sa;

            string ss;

            sa = new string[10000000];

            for (int i = 0; i < 10000000; i++)

                sa[i] = "This is a string";

            foreach (string s in sa)

                ss = s;

        }

    }

}

　　然后是测试结果：

所以当需要改善性能的时候，不仅需要用for，而且最好是用连续的存储空间类型的集合。